Bob's age is 38 and his son"s age is 4. In how many years' time will Bob's age be twicethe age of his son?

38+x = 2(4+x)

38+x = 8 +2x
38-8 = 2x - x
30 = x
So, His age is 30+38 = 68
His son age is 30 + 4 = 34
difference is 68-34 = 30